Power overlay structure and method of making same

ABSTRACT

A power overlay (POL) structure includes a POL sub-module. The POL sub-module includes a dielectric layer and a semiconductor device having a top surface attached to the dielectric layer. The top surface of the semiconductor device has at least one contact pad formed thereon. The POL sub-module also includes a metal interconnect structure that extends through the dielectric layer and is electrically coupled to the at least one contact pad of the semiconductor device. A conducting shim is coupled to a bottom surface of the semiconductor device and a first side of a thermal interface is coupled to the conducting shim. A heat sink is coupled to a second side of the electrically insulating thermal interface.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/784,834 filed Mar. 14, 2013, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to structures and methods for packaging semiconductor devices and, more particularly, to a power overlay (POL) packaging structure that includes an improved thermal interface.

Power semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits, such as switched mode power supplies, for example. Most power semiconductor devices are only used in commutation mode (i.e., they are either on or off), and are therefore optimized for this. Many power semiconductor devices are used in high voltage power applications and are designed to carry a large amount of current and support a large voltage. In use, high voltage power semiconductor devices are connected to an external circuit by way of a power overlay (POL) packaging and interconnect system.

The general structure of a prior art power overlay (POL) structure 10 is shown in FIG. 1. The standard manufacturing process for the POL structure 10 typically begins with placement of one or more power semiconductor devices 12 onto a dielectric layer 14 by way of an adhesive 16. Metal interconnects 18 (e.g., copper interconnects) are then electroplated onto dielectric layer 14 to form a direct metallic connection to the power semiconductor devices 12. The metal interconnects 18 may be in the form of a low profile (e.g., less than 200 micrometers thick), planar interconnect structure that provides for formation of an input/output (I/O) system 20 to and from the power semiconductor devices 12. For connecting to an external circuit, such as by making a second level interconnection to a printed circuit board for example, current POL packages use solder ball grid arrays (BGAs) or land grid arrays (LGAs).

A heat sink 22 is also typically included in the POL structure 10 to providing a way to remove the heat generated by semiconductor devices 12 and protect the devices 12 from the external environment. Heat sink 22 is thermally coupled to the devices 12 using a direct bond copper (DBC) substrate 24. As shown, DBC substrate 24 is positioned between the upper surfaces of semiconductor devices 12 and the lower surface of heat sink 22.

DBC substrate 24 is a prefabricated component that includes a non-organic ceramic substrate 26 such as, for example, alumina, with upper and lower sheets of copper 28, 30 bonded to both sides thereof via a direct bond copper interface or braze layer 31. The lower copper sheet 30 of DBC substrate 24 is patterned to form a number of conductive contact areas before DBC substrate 24 is attached to semiconductor devices 12. A typically DBC substrate may have an overall thickness of approximately 1 mm.

During the fabrication process of POL structure 10, solder 32 is applied to the surfaces of semiconductor devices 12. DBC substrate 24 is then lowered onto solder 32 to align the patterned portions of lower copper sheet 30 with solder 32. After DBC substrate 24 is coupled to semiconductor devices 12, an underfill technique is used to apply a dielectric organic material 34 in the space between adhesive layer 16 and DBC substrate 24 to form a POL sub-module 36. A thermal pad or thermal grease 38 is then applied to the upper copper layer 28 of DBC substrate 24.

The use of a DBC substrate in a POL structure 10 has a number of limitations. First, the material properties of the copper and ceramic materials of the DBC substrate place inherent limitations on the design of the DBC substrate. For example, due to the inherent stiffness of ceramics and the differences in the thermal expansion coefficients of the copper and ceramic materials of DBC substrate 24, copper sheets 28, 30 must be kept relatively thin to avoid undue stresses placed on the ceramics caused by large swings in temperature in the copper material. In addition, since the surface of the lower copper layer of the DBC substrate 24 that faces semiconductor device(s) 12 is planar, the DBC substrate 24 does not facilitate fabrication of a POL package having semiconductor devices of differing height.

Also, DBC substrates are relatively expensive to manufacture and are a prefabricated component. As DBC substrate 24 is a prefabricated component, the thickness of copper sheets 28, 30 is predetermined based on the thickness of the copper foil layer applied to the ceramic substrate 26. Also, because DBC substrate 24 is fabricated prior to assembly with the remainder of the components of the POL structure, the dielectric filler or epoxy substrate that surrounds the semiconductor devices 12 is applied using an underfill technique after the DBC substrate 24 is coupled to semiconductor devices 12. This underfill technique is time consuming and can result in undesirable voids within the POL structure.

Therefore, it would be desirable to provide a POL structure having an improved thermal interface that overcomes the aforementioned structural and processing limitations of known POL structures that incorporate a DBC substrate. It would further be desirable for such a POL structure to account for semiconductor devices of different thickness while minimizing cost of the POL structure.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention overcome the aforementioned drawbacks by providing a power overlay (POL) structure that eliminates the usage of a DBC substrate as a thermal interface between a POL sub-module and a heat sink. An improved thermal interface is provided between semiconductor devices and the heat sink that includes conducting shims that account for semiconductor devices of varying heights.

In accordance with one aspect of the invention, a power overlay (POL) structure includes a POL sub-module. The POL sub-module includes a dielectric layer and a semiconductor device having a top surface attached to the dielectric layer. The top surface of the semiconductor device has at least one contact pad formed thereon. The POL sub-module also includes a metal interconnect structure that extends through the dielectric layer and is electrically coupled to the at least one contact pad of the semiconductor device. A conducting shim is coupled to a bottom surface of the semiconductor device and a first side of a thermal interface is coupled to the conducting shim. A heat sink is coupled to a second side of the electrically insulating thermal interface.

In accordance with another aspect of the invention, a method of forming a power overlay (POL) structure includes providing a semiconductor device, affixing a first surface of the semiconductor device to a dielectric layer, forming vias through the dielectric layer and forming a metal interconnect structure extending through the vias in the dielectric layer to electrically connect to the semiconductor device. The method also includes affixing a first surface of a conductive shim to a second surface of the semiconductor device and forming a thermal interface atop a second surface of the conductive shim. Further, the method includes thermally coupling a heat sink to the conductive shim absent a direct bond copper (DBC) substrate positioned between the heat sink and the conductive shim.

In accordance with yet another aspect of the invention, a power overlay (POL) packaging structure includes a POL sub-module. The POL sub-module includes a dielectric layer, a first semiconductor device attached to the dielectric layer, and an interconnect structure electrically coupled to a first side of the first semiconductor device. The interconnect structure extends through the dielectric layer to electrically connect to at least one contact pad on the first semiconductor device. A first conducting shim has a bottom surface coupled to a second side of the first semiconductor device and a thermal interface coupled to a top surface of the first conducting shim absent a direct bond copper (DBC) substrate positioned therebetween. A heat sink is directly coupled to the thermal interface.

In accordance with yet another aspect of the invention, a semiconductor device package includes a first semiconductor device, a second semiconductor device having a thickness that is greater than a thickness of the first semiconductor device, and an insulating substrate coupled to first surfaces of the first and second semiconductor devices. A metallization layer extends through the insulating substrate such that a first surface of the metallization layer is coupled to the contact pads of the first and second semiconductor devices. A first conducting shim having a first side is coupled to the first semiconductor device via a conductive contact layer; a second conducting shim having a first side is coupled to the first semiconductor device via the conductive contact layer. The first conducting shim has a thickness that is greater than a thickness of the second conducting shim and second sides of the first and second conducting shims are co-planar.

In accordance with yet another aspect of the invention, a semiconductor device package includes a dielectric layer having a plurality of vias formed therethrough and a semiconductor device having a first surface coupled to a top surface of the dielectric layer. The semiconductor device package also includes a metal interconnect structure coupled to a bottom surface of the dielectric layer. The metal interconnect structure extends through the plurality of vias of the dielectric layer to connect to the first surface of the semiconductor device. The semiconductor device package also includes a conducting shim having a bottom surface coupled to a second surface of the semiconductor device and an organic thermal interface coupled to a top surface of the conducting shim absent a direct bond copper (DBC) substrate positioned between the organic thermal interface and the conducting shim.

These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carrying out the invention.

In the drawings:

FIG. 1 is a schematic cross-sectional side view of a prior art power overlay (POL) structure incorporating a DBC substrate.

FIG. 2 is a schematic cross-sectional side view of a POL structure according to an embodiment of the invention.

FIG. 3 is a schematic cross-sectional side view of a POL structure according to another embodiment of the invention.

FIG. 4 is a schematic cross-sectional side view of a POL structure according to yet another embodiment of the invention.

FIG. 5 is a schematic cross-sectional side view of a POL assembly according to an embodiment of the invention.

FIGS. 6-16 are schematic cross-sectional side views of a POL sub-module during various stages of a manufacturing/build-up process according to embodiments of the invention.

FIG. 17 is a schematic cross-sectional side view of a portion of a leaded POL sub-module according to another embodiment of the invention.

FIG. 18 is a schematic cross-sectional side view of a portion of a leaded POL sub-module according to another embodiment of the invention.

FIG. 19 is a schematic cross-sectional side view of a portion of a POL sub-module having a stepped conducting shim according to an embodiment of the invention.

FIG. 20 is a schematic cross-sectional side view of a portion of a POL sub-module having a multi-layer conducting shim assembly according to an embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide for a power overlay (POL) structure having an improved thermal interface included therein, as well as a method of forming such a POL structure. The POL structure includes conducting shims that account for semiconductor devices of varying heights and a thermal interface layer that increases options for encapsulation materials and methods.

Referring to FIG. 2, a semiconductor device assembly or power overlay (POL) structure 40 is shown according to an embodiment of the invention. POL structure 40 includes a POL sub-module 42 having one or more semiconductor devices 43, 44, 45 therein that, according to various embodiments, may be in the form of a die, diode, or other power electric device. As shown in FIG. 2, three semiconductor devices 43, 44, 45 are provided in POL sub-module 42, however, it is recognized that a greater or lesser number of semiconductor devices 43, 44, 45 could be included in POL sub-module 42. In addition to semiconductor devices 43, 44, 45, POL sub-module 42 may also include any number of additional circuitry components 46 such as, for example, a gate driver.

Semiconductor devices 43, 44, 45 are coupled to a dielectric layer 48 by way of an adhesive layer 50. Dielectric layer 48 may be in the form of a lamination or a film, according to various embodiments, and may be formed of one a plurality of dielectric materials, such as Kapton®, UItem®, polytetrafluoroethylene (PTFE), Upilex®, polysulfone materials (e.g., Udel®, Radel®), or another polymer film, such as a liquid crystal polymer (LCP) or a polyimide material.

POL sub-module 42 also includes a metallization layer or interconnect structure 52, which forms a direct metallic connection to semiconductor devices 43, 44, 45 by way of a metal interconnects 54 that extends through vias 56 formed in dielectric layer 48 to connect to contact pads 58 on respective semiconductor devices 43, 44, 45.

POL sub-module 42 further includes one or more conducting slabs or shims 60, which are secured to semiconductor devices 43, 44, 45 with a thermally and electrically conductive contact layer 62. According to various embodiments, conductive contact layer 62 may be a solder material, a conductive adhesive, or a sintered silver, as examples. Conducting shims 60 are a metal or alloy material, such as, for example, copper, aluminum, molybdenum, or combinations thereof such as copper-molybdenum or copper-tungsten, and composites such as aluminum-silicon, aluminum-silicon carbide, aluminum-graphite, copper-graphite and the like.

A dielectric filler material 64 is also provided in POL sub-module 42 to fill gaps in the POL sub-module 42 between and around semiconductor devices 43, 44, 45 and conducting shims 60, so as to provide additional structural integrity to POL sub-module 42. According to various embodiments, dielectric filler material 64 may be in the form of a polymeric material, such as, for example, an underfill (e.g., capillary underfill or no-flow underfill), encapsulate, silicone, or a molding compound.

POL structure 40 also includes a heat sink 66 to facilitate cooling of semiconductor devices 43, 44, 45. Heat sink 66 comprises a material having a high thermal conductivity, such as copper, aluminum, or a composite material. Heat sink 66 is coupled to POL sub-module 42 by way of a thermal interface substrate or layer 68 formed over conducting shims 60 and dielectric filler material 64.

Thermal interface layer 68 is a thermally conductive, electrically insulating polymeric or organic material such as, for example, a thermal pad, a thermal paste, a thermal grease, or a thermal adhesive. Thermal interface layer 68 electrically isolates heat sink 66 from conducting shims 60. According to one embodiment, thermal interface layer 68 comprises conductive fillers, particles, or fibers suspended in a matrix of resin or epoxy. For example, thermal interface layer 68 may be an epoxy or silicon resin that is filled with thermally conductive, electrically insulating fillers such as alumina and/or boron nitride. According to one embodiment, thermal interface layer 68 has a thickness of approximately 100 μm. However, one skilled in the art will recognize that the thickness of thermal interface layer 68 may vary based on design specifications. Thermal interface layer 68 provides superior thermal performance as compared to a DBC substrate because thermal interface layer 68 is not subject to the thermal resistance of the ceramic layer included within DBC substrate.

In embodiments where thermal interface layer 68 is a thermal paste, a thermal grease, or a thermal pad, such as, for example a pre-formed sheet or film of organic material, heat sink 66 is secured to POL sub-module 42 using screws or other fastening devices (not shown), at a number of locations around the perimeter of POL sub-module 42 causing thermal interface layer 68 to be sandwiched between conducting shims 60 and heat sink 66. Alternatively, in embodiments where thermal interface layer 68 is a polymeric adhesive, thermal interface layer 68 is applied to POL sub-module 42 in a tacky state and cured after heat sink 66 is positioned atop thermal interface layer 68, thereby bonding heat sink 66 to POL sub-module 42 absent additional fasteners.

POL sub-module 42 also includes an input-output (I/O) connection 70 to enable surface mounting of the POL structure 40 to an external circuit, such as a printed circuit board (PCB), as described in more detail with respect to FIG. 5. According to an exemplary embodiment, I/O connection 70 is formed of ball grid array (BGA) solder bumps 72 that are configured to be attached/affixed to the PCB to electrically couple POL structure 40 to the PCB, although other suitable second-level solder interconnections, such as land grid array (LGA) pads, could also be used. The BGA solder bumps 72 provide a highly reliable interconnection structure that is resistive to failure in high stress conditions. As illustrated in FIG. 2, solder bumps 72 are positioned in openings formed in a solder mask layer 74 of POL sub-module 42.

Referring now to FIG. 3, a POL structure 76 and POL sub-module 78 are shown according an alternative embodiment of the invention. POL structure 76 and POL sub-module 78 include a number of components similar to components shown in POL structure 40 and POL sub-module 42 of FIG. 2, and thus numbers used to indicate components in FIG. 2 will also be used to indicate similar components in FIG. 3.

As shown, POL sub-module 78 includes a multi-layer thermal interface 80 positioned between conducting shims 60 and heat sink 66. Multi-layer thermal interface 80 includes a first thermal interface layer 82, a ceramic insulator layer 84, and a second thermal interface layer 86. The inclusion of ceramic insulator layer 84 between POL sub-module 78 and heat sink 66 provides additional electrical isolation for high voltage applications. Insulator layer 84 may be constructed of a ceramic material such as alumina or aluminum nitride, as examples.

As shown, first thermal interface layer 82 is sandwiched between conducting shims 60 and ceramic insulator layer 84. According to one embodiment first thermal interface layer 82 of FIG. 3 comprises a thermally conductive, electrically insulating material similar to thermal interface layer 68 of FIG. 2 that permits the transfer of heat from conducting shims 60 to heat sink 66 while electrically isolating conducting shims 60 from heat sink 66. In an exemplary embodiment, first thermal interface layer 82 comprises an epoxy or silicon resin that is filled with thermally conductive but electrically insulating fillers such as alumina or boron nitride.

In an alternative embodiment, first thermal interface layer 82 comprises an electrically conductive material, such as, for example, solder, conductive adhesive, or sintered silver, formed as a number of discrete pads 88 atop conducting shims 60, as illustrated in FIG. 4. Lateral spaces 90 between adjoining pads 88 may be left as air gaps or be filled with dielectric filler material 64, according to various embodiments.

Referring now to FIG. 3 and FIG. 4 together, second thermal interface layer 86 is sandwiched between ceramic insulator layer 84 and heat sink 66. According to one embodiment, second thermal interface layer 86 comprises a thermally conductive, electrically insulating material similar to thermal interface layer 68 of FIG. 2. In an alternative embodiment, second thermal interface layer 86 is a material that is both thermally and electrically conductive, such as, for example, an epoxy or silicon resin filled with silver.

FIG. 5 illustrates a POL assembly 92 incorporating POL structure 40 (FIG. 2) and POL structure 76 (FIGS. 3, 4) in accordance with an embodiment of the invention. As shown, respective I/O connections 70 of POL structures 40, 76 are coupled to an external circuit component 94, such as, for example, a printed circuit board (PCB). While two POL structures 40, 76 are illustrated in POL assembly 92, one skilled in the art will recognize that POL assembly 92 may include any number of POL structures, according to various embodiments of the invention. Further, POL assembly 92 may include multiple POL structures of a single type, such as two or more POL structures 40 or two or more POL structures 76.

Referring now to FIGS. 6-16, detailed views of the process steps for a technique of manufacturing POL sub-module 42 of FIG. 2 and POL sub-module 78 of FIGS. 3 and 4 are provided, according to an embodiment of the invention. Referring first to FIG. 6, the build-up process of POL sub-module 42, 78 begins with applying an adhesive layer 50 onto dielectric layer 48. In a next step of the technique, one or more semiconductor device(s) 44, 45 (e.g., two semiconductor devices) are secured to dielectric layer 48 by way of adhesive layer 50, as illustrated in FIG. 7. To secure the semiconductor devices 44, 45 to dielectric layer 48, the top surfaces 96 of semiconductor devices 44, 45 are placed onto adhesive layer 50. Adhesive 50 is then cured to secure semiconductor devices 44, 45 onto dielectric layer 48.

A plurality of vias 56 is then formed through adhesive layer 50 and dielectric layer 48, as illustrated in FIG. 8. According to embodiments of the invention, vias 56 may be formed by way of a laser ablation or laser drilling process, plasma etching, photo-definition, or mechanical drilling processes.

While the formation of vias 56 through adhesive layer 50 and dielectric layer 48 is shown in FIG. 8 as being performed after placement of semiconductor devices 44, 45 onto adhesive layer 50, it is recognized that the placement of semiconductor devices 44, 45 could occur after to via formation. Alternately, depending on constraints imposed by via size, semiconductor devices 44, 45 could first be placed on adhesive layer 50 and dielectric layer 48, with the vias 56 subsequently being formed at locations corresponding to a plurality of metalized circuits and/or connection pads contact pads 58 formed on semiconductor devices 44, 45. Furthermore, a combination of pre- and post-drilled vias could be employed.

Referring now to FIGS. 9 and 10, upon securing of semiconductor devices 44, 45 on the dielectric layer 48 and the formation of vias 56, the vias 56 are cleaned (such as through a reactive ion etching (RIE) desoot process) and subsequently metalized to form a metallization or interconnection layer 54. Metallization layer 54 is typically formed through a combination of sputtering and electroplating applications, although it is recognized that other electroless methods of metal deposition could also be used. For example, a titanium adhesion layer and copper seed layer may first be applied via a sputtering process, followed by an electroplating process that increases a thickness of the copper to a desired level. The applied metal material is then subsequently patterned into metal interconnects 54 having a desired shape and that function as vertical feed-throughs formed through dielectric layer 48 and adhesive layer 50. Metal interconnects 54 extend out from circuits and/or connection pads contact pads 58 of semiconductor devices 44, 45, through vias/opening 56, and out across a top surface 98 of dielectric layer 48.

As shown in FIG. 11, a solder mask layer 74 is applied over the patterned metal interconnects 54 to provide a protective coating and define interconnect pads. In an alternative embodiment, it is recognized that that the interconnect pads can have a metal finish to aid solderability, such as Ni or Ni/Au.

Referring now to FIG. 12, in a next step of the fabrication technique, a conductive contact layer 62 is applied to a bottom surface 100 of semiconductor devices 44, 45. A bottom surface 102 of conducting shims 60 are then coupled to semiconductor device 44, 45 by way of the conductive contact layer 62.

According to one embodiment of the invention, and as shown in FIG. 12, semiconductor devices 44, 45 may be of varying thickness/height. In order to equalize the overall height of respective semiconductor devices 44, 45, conducting shims 60 may be of differing height so that the overall thickness/height of each semiconductor devices 44, 45/conducting shim pair 60 is equal and a back surface of the conducting shims 60 is “planarized.”

As shown in FIG. 13, the build-up technique of manufacturing POL sub-module 42, 78 continues with the application of a dielectric filler material 64 to fill in gaps in POL sub-module 42, 78 between and around semiconductor devices 44, 45 and conducting shims 60, so as to constrain dielectric layer 48 and provide additional electrical insulation and structural integrity to POL sub-module 42, 78. In one embodiment, dielectric filler material 64 is applied using an overmolding technique and cured. After dielectric filler material 64 is cured, a portion 104 of dielectric filler material 64 is removed using a grinding operation to expose conducting shim 60. This grinding operation may also be used to remove any variation in the height of conducting shims 60 so that a top surface 106 of conducting shims 60 and a top surface top surface 108 of dielectric filler material 64 is coplanar, as shown in FIG. 14. Alternatively, an overmolding or encapsulating technique may be used to apply dielectric filler material 64 such that the top surface 108 of the cured dielectric filler material 64 is flush with the top surface 106 of conducting shims 60 absent a grinding step. In yet another embodiment, dielectric filler material 64 may be applied using an underfill technique.

In a next step of the fabrication process, a first side 110 of a thermal interface 112 is applied to respective top surfaces 106, 108 of conducting shims 60 and dielectric filler material 64, as shown in FIG. 15. In embodiments where thermal interface 112 comprises single thermal interface layer 68 (FIG. 2), thermal interface 112 is applied in one step to the top surfaces 106, 108 of conducting shims 60 and dielectric filler material 64. Alternatively, thermal interface 112 may be a multi-layer thermal interface 80 as shown in FIGS. 3 and 4. Referring as well to FIGS. 3 and 4, the individual layers of multi-layer thermal interface 80 are applied sequentially to the top surfaces 106, 108 of conducting shims 60 and dielectric filler material 64 using a build-up technique wherein first thermal interface layer 82 is applied atop dielectric filler material 64 and conducting shims 60, ceramic insulator layer 84 is next applied atop first thermal interface layer 82, and second thermal interface layer 86 is finally applied to the top surface of ceramic insulator layer 84.

In a next step of the fabrication technique, I/O connections 70 are applied to solder mask layer 74. In one embodiment, I/O connections 70 are solder bumps 72, as shown in FIG. 16. In an alternative embodiment of the build-up technique, I/O connections 70 are configured as leads 114 for a through-hole component, as shown in FIG. 17. After the build-up process of POL sub-module 42, 78 is complete, a heat sink 66 is affixed to a second side 116 of thermal interface 112. POL sub-module 42, 78 may be singulated for surface mounting to an external circuit, such as PCB 94 (FIG. 5).

Referring now to FIG. 18, an alternative embodiment of a POL sub-module 118 is illustrated. POL sub-module 118 includes a number of components similar to components shown in POL sub-module 42 of FIG. 2, and thus numbers used to indicate components in FIG. 2 will also be used to indicate similar components in FIG. 18.

As shown, POL sub-module 118 includes semiconductor device(s) 44 mounted to a dielectric layer 48 by way of an adhesive layer 50. Metal interconnects 54 extend through vias 56 formed in dielectric layer 48 to connect to contact pads (not shown) on semiconductor device(s) 44. A conducting shim 120 is coupled to each semiconductor device 44 by way of a conductive contact layer 62. Similar to conducting shims 60 of FIG. 2, conducting shims 120 comprise a metal or alloy material, such as, for example, copper, aluminum, molybdenum, or combinations thereof. Dielectric filler material 64 is provided to fill gaps in POL sub-module 118 between and around semiconductor devices 44 and conducting shims 120. A thermal interface 112, such as thermal interface layer 68 (FIG. 2) or multi-layer thermal interface 80 (FIG. 3), is provided atop dielectric filler material 64 and conducting shims 120.

As shown in FIG. 18, conducting shims 120 are coupled to a lead-frame 122. According to embodiments of the invention, lead-frame 122 is pre-attached to conducting shim 120 prior to placement of conducting shims 120 into conductive contact layer 62. For example, lead-frame 122 and conducting shims 60 may be a prefabricated from a common copper slab or lead-frame 122 may be pre-attached to conducting shims 60 by way of a high temperature joining process like soldering, brazing, welding, or other similar method for assembly into POL sub-module 118. Alternatively, it is recognized that lead-frame 122 may be post-attached instead, after fabrication of POL sub-module 118 is completed.

Referring now to FIGS. 19 and 20, two alternative embodiments of a POL sub-module 124 are illustrated that account for situations wherein POL sub-module 124 includes semiconductor devices 126, 128 of differing heights. Again, as POL sub-module 124 includes a number of components similar to components shown in POL sub-module 42 of FIG. 2, and thus numbers used to indicate components in FIG. 2 will also be used to indicate similar components in FIGS. 19 and 20.

Referring first to FIG. 19, an alternative embodiment is shown that includes a conducting shim 130 having a stepped configuration. As shown, a first portion 132 of conducting shim 130 has a first height or thickness 134 and a second portion 136 of conducting shim 130 has a second height or thickness 138 to account for the differing heights of semiconductor devices 126, 128 while maintaining a planar top surface 140 of conducting shim 130.

An alternative embodiment of POL sub-module 124 is shown in FIG. 20, wherein a first conducting shim 142 is coupled to semiconductor device 126 using a first conductive contact layer 144, such as, for example, a solder similar to conductive contact layer 62 (FIG. 2). First conducting shim 142 is sized such that an upper surface 146 of first conducting shim 142 and an upper surface 148 of semiconductor device 128 are coplanar. A second conductive contact layer 150 is then applied to the top surfaces of first conducting shim 142 and semiconductor device 128. In one embodiment, second conductive contact layer 150 comprises solder. A second conducting shim 152, which is sized to span at least the overall width of semiconductor devices 126, 128 is then affixed to second conducting shim 152 as shown.

Beneficially, embodiments of the invention thus provide a POL packaging and interconnect structure that includes a thermal interface that is absent the drawbacks of a DBC substrate. For example, as thermal interface layer 68 and multi-layer thermal interface 80 may be applied in a fabrication step that occurs after dielectric filler material 64 is applied and cured, dielectric filler material 64 may be applied using an encapsulating or overmolding technique rather than a more costly and time-consuming underfill process that is more likely to result in voids. Also, because the thermal interface is formed during the package build-up process, rather than being provided as a prefabricated component, the dimensions and materials of thermal interface may be tailored based on desired operating characteristics. Further, the use of conducting shims 60, 120, 130, 142, and/or 152 provides the ability to account for semiconducting devices of varying heights.

While embodiments of the invention have been described as including power semiconductor devices used in high voltage power applications, one skilled in the art will recognize that the techniques set forth herein are equally applicable to low power applications and chip packages that incorporate non-power semiconductor devices or semiconductor devices having electrical connections that run to only a single side of the semiconductor devices.

Therefore, according to one embodiment of the invention, a power overlay (POL) structure includes a POL sub-module. The POL sub-module includes a dielectric layer and a semiconductor device having a top surface attached to the dielectric layer. The top surface of the semiconductor device has at least one contact pad formed thereon. The POL sub-module also includes a metal interconnect structure that extends through the dielectric layer and is electrically coupled to the at least one contact pad of the semiconductor device. A conducting shim is coupled to a bottom surface of the semiconductor device and a first side of a thermal interface is coupled to the conducting shim. A heat sink is coupled to a second side of the electrically insulating thermal interface.

According to another embodiment of the invention, a method of forming a power overlay (POL) structure includes providing a semiconductor device, affixing a first surface of the semiconductor device to a dielectric layer, forming vias through the dielectric layer and forming a metal interconnect structure extending through the vias in the dielectric layer to electrically connect to the semiconductor device. The method also includes affixing a first surface of a conductive shim to a second surface of the semiconductor device and forming a thermal interface atop a second surface of the conductive shim. Further, the method includes thermally coupling a heat sink to the conductive shim absent a direct bond copper (DBC) substrate positioned between the heat sink and the conductive shim.

According to yet another embodiment of the invention, a power overlay (POL) packaging structure includes a POL sub-module. The POL sub-module includes a dielectric layer, a first semiconductor device attached to the dielectric layer, and an interconnect structure electrically coupled to a first side of the first semiconductor device. The interconnect structure extends through the dielectric layer to electrically connect to at least one contact pad on the first semiconductor device. A first conducting shim has a bottom surface coupled to a second side of the first semiconductor device and a thermal interface coupled to a top surface of the first conducting shim absent a direct bond copper (DBC) substrate positioned therebetween. A heat sink is directly coupled to the thermal interface.

According to yet another embodiment of the invention, a semiconductor device package includes a first semiconductor device, a second semiconductor device having a thickness that is greater than a thickness of the first semiconductor device, and an insulating substrate coupled to first surfaces of the first and second semiconductor devices. A metallization layer extends through the insulating substrate such that a first surface of the metallization layer is coupled to the contact pads of the first and second semiconductor devices. A first conducting shim having a first side is coupled to the first semiconductor device via a conductive contact layer; a second conducting shim having a first side is coupled to the first semiconductor device via the conductive contact layer. The first conducting shim has a thickness that is greater than a thickness of the second conducting shim and second sides of the first and second conducting shims are co-planar.

According to yet another embodiment of the invention, a semiconductor device package includes a dielectric layer having a plurality of vias formed therethrough and a semiconductor device having a first surface coupled to a top surface of the dielectric layer. The semiconductor device package also includes a metal interconnect structure coupled to a bottom surface of the dielectric layer. The metal interconnect structure extends through the plurality of vias of the dielectric layer to connect to the first surface of the semiconductor device. The semiconductor device package also includes a conducting shim having a bottom surface coupled to a second surface of the semiconductor device and an organic thermal interface coupled to a top surface of the conducting shim absent a direct bond copper (DBC) substrate positioned between the organic thermal interface and the conducting shim.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

What is claimed is:
 1. A power overlay (POL) structure comprising: a POL sub-module, the POL sub-module comprising: a dielectric layer; a semiconductor device having a top surface attached to the dielectric layer, the top surface having at least one contact pad formed thereon; a metal interconnect structure extending through the dielectric layer and electrically coupled to the at least one contact pad of the semiconductor device; a conducting shim coupled to a bottom surface of the semiconductor device; and a thermal interface having a first side coupled to the conducting shim; and a heat sink coupled to a second side of the electrically insulating thermal interface.
 2. The POL structure of claim 1 wherein the thermal interface is thermally conductive.
 3. The POL structure of claim 1 further comprising an encapsulate positioned around the semiconductor device and the conducting shim in a space between the dielectric layer and the thermal interface.
 4. The POL structure of claim 1 wherein the thermal interface is coupled to the conducting shim absent a direct bond copper (DBC) substrate positioned therebetween.
 5. The POL structure of claim 1 wherein the conducting shim comprises at least one of copper, molybdenum, and aluminum.
 6. The POL structure of claim 1 further comprising one of a solder material, a conductive adhesive, and a sintered silver layer positioned between the semiconductor device and the conducting shim to secure the conducting shim to the semiconductor device.
 7. The POL structure of claim 1 further comprising a printed circuit board; and wherein the POL sub-module is attached to the printed circuit board by way of an input/output connection.
 8. The POL structure of claim 1 further comprising a lead-frame electrically coupled to the POL sub-module; and wherein the lead-frame is attached directly to the conducting shim.
 9. A method of forming a power overlay (POL) structure comprising: providing a semiconductor device; affixing a first surface of the semiconductor device to a dielectric layer; forming vias through the dielectric layer; forming a metal interconnect structure extending through the vias in the dielectric layer to electrically connect to the semiconductor device; affixing a first surface of a conductive shim to a second surface of the semiconductor device; forming a thermal interface atop a second surface of the conductive shim; and thermally coupling a heat sink to the conductive shim absent a direct bond copper (DBC) substrate positioned between the heat sink and the conductive shim.
 10. The method of claim 9 further comprising encapsulating the semiconductor device and at least a portion of the conductive shim with a polymeric molding compound prior to forming the thermal interface.
 11. The method of claim 9 further comprising applying an underfill between the dielectric layer and the thermal interface to encapsulate the semiconductor device and at least a portion of the conductive shim.
 12. The method of claim 9 wherein forming the thermal interface comprises coating the top surface of the conducting shim with one of a thermal conductive liquid and a thermally conductive paste.
 13. The method of claim 12 further comprising curing the thermal interface.
 14. The method of claim 9 further comprising affixing the first surface of the conductive shim to the second surface of the semiconductor device using a conductive paste.
 15. The method of claim 9 further comprising attaching the metal interconnect structure to an external circuit structure.
 16. The method of claim 9 further comprising providing a lead-frame assembly coupled to the conductive shim, the lead-frame forming an interconnection between the POL structure and an external circuit structure.
 17. A power overlay (POL) packaging structure comprising: a POL sub-module, the POL sub-module comprising: a dielectric layer; a first semiconductor device attached to the dielectric layer; an interconnect structure electrically coupled to a first side of the first semiconductor device, the interconnect structure extending through the dielectric layer to electrically connect to at least one contact pad on the first semiconductor device; a first conducting shim having a bottom surface coupled to a second side of the first semiconductor device; and a thermal interface coupled to a top surface of the first conducting shim absent a direct bond copper (DBC) substrate positioned therebetween; and a heat sink directly coupled to the thermal interface.
 18. The POL packaging structure of claim 17 wherein the first conducting shim comprises copper.
 19. The POL packaging structure of claim 17 further comprising a filler material surrounding the first semiconductor device and at least a portion of the first conducting shim.
 20. The POL packaging structure of claim 17 further comprising a second semiconductor device having a first side attached to the dielectric layer.
 21. The POL packaging structure of claim 20 wherein the bottom side of the first conducting shim is coupled to a second side of the second semiconductor device.
 22. The POL packaging structure of claim 21 wherein the second semiconductor device has a vertical height different than a vertical height of the first semiconductor device; wherein a first portion of the first conducting shim is coupled to the first semiconductor device; wherein a second portion of the first conducting shim is coupled to the second semiconductor device; and wherein an overall vertical height of the first portion of the first conducting shim and the first semiconductor device is substantially equal to an overall vertical height of the second portion of the first conducting shim and the second semiconductor device.
 23. The POL packaging structure of claim 20 further comprising a second conducting shim having a bottom surface coupled to the second semiconductor device.
 24. The POL packaging structure of claim 20 further comprising: a printed circuit board; and a lead-frame coupled to the first conductive shim, the lead-frame configured to electrically connect the POL sub-module to the printed circuit board.
 25. A semiconductor device package comprising: a first semiconductor device; a second semiconductor device having a thickness that is greater than a thickness of the first semiconductor device; an insulating substrate coupled to first surfaces of the first and second semiconductor devices; a metallization layer extending through the insulating substrate such that a first surface of the metallization layer is coupled to the contact pads of the first and second semiconductor devices; a first conducting shim having a first side coupled to the first semiconductor device via a conductive contact layer, a second conducting shim having a first side coupled to the second semiconductor device via the conductive contact layer; and wherein the first conducting shim has a thickness that is greater than a thickness of the second conducting shim; and wherein second sides of the first and second conducting shims are co-planar.
 26. The semiconductor device package of claim 25 further comprising a thermal interface layer coupled to a second side of the first conducting shim and a second side of the second conducting shim.
 27. The semiconductor device package of claim 26 wherein the thermal interface layer is electrically insulating and thermally conductive.
 28. The semiconductor device package of claim 26 wherein the thermal interface layer is electrically conductive and thermally conductive.
 29. The semiconductor device package of claim 26 wherein the thermal interface layer comprises a plurality of conductive fibers suspended in a matrix of resin.
 30. The semiconductor device package of claim 26 wherein a first portion of the thermal interface layer is coupled to the first conducting shim and a second portion of the thermal interface layer is coupled to the second conducting shim; and wherein a gap is formed between the first and second portions of the thermal interface layer such that the first portion of the thermal interface layer is electrically isolated from the second portion of the thermal interface layer.
 31. The semiconductor device package of claim 26 wherein the thermal interface layer comprises a multi-layer substrate, the multi-layer substrate comprising: a first thermal interface layer comprising an electrically insulating and thermally conductive material having a first side directly coupled to the first and second conducting shims; a ceramic substrate having a first side directly coupled to a second side of the first thermal interface layer; and a second thermal interface layer comprising an electrically insulating and thermally conductive material directly coupled to a second side of the ceramic substrate.
 32. The semiconductor device package of claim 26 wherein the thermal interface layer comprises a multi-layer substrate, the multi-layer substrate comprising: a first thermal interface layer comprising an electrically insulating and thermally conductive material having a first side directly coupled to the first and second conducting shims; a ceramic substrate having a first side directly coupled to a second side of the first thermal interface layer; and a second thermal interface layer comprising an electrically conductive and thermally conductive material directly coupled to a second side of the ceramic substrate.
 33. A semiconductor device package comprising: a dielectric layer having a plurality of vias formed therethrough; a semiconductor device having a first surface coupled to a top surface of the dielectric layer; a metal interconnect structure coupled to a bottom surface of the dielectric layer, the metal interconnect structure extending through the plurality of vias of the dielectric layer to connect to the first surface of the semiconductor device; a conducting shim having a bottom surface coupled to a second surface of the semiconductor device; and an organic thermal interface coupled to a top surface of the conducting shim absent a direct bond copper (DBC) substrate positioned between the organic thermal interface and the conducting shim.
 34. The semiconductor device package of claim 33 wherein the organic thermal interface is thermally conductive and electrically conductive.
 35. The semiconductor device package of claim 33 wherein the organic thermal interface is thermally conductive and electrically insulating.
 36. The semiconductor device package of claim 33 wherein the organic thermal interface comprises a plurality of conductive fibers suspended in a matrix of resin.
 37. The semiconductor device package of claim 33 further comprising an insulating underfill material located between the dielectric layer and the thermal interface.
 38. The semiconductor device package of claim 33 wherein the conducting shim comprises a thermally and electrically conductive material.
 39. The semiconductor device package of claim 33 wherein the organic thermal interface comprises a multi-layer substrate, the multi-layer substrate comprising: a first layer comprising an organic material having a first side coupled to the conducting shim; a ceramic substrate having a first side directly coupled to a second side of the first layer; and a second layer comprising an electrically insulating and thermally conductive material directly coupled to a second side of the ceramic substrate.
 40. The semiconductor device package of claim 33 wherein the organic thermal interface comprises a multi-layer substrate, the multi-layer substrate comprising: a first layer comprising an organic material having a first side coupled to the conducting shim; a ceramic substrate having a first side directly coupled to a second side of the first layer; and a second layer comprising an electrically and thermally conductive material directly coupled to a second side of the ceramic substrate.
 41. The POL packaging structure of claim 1 wherein the conducting shim comprises one of a metal and an alloy material.
 42. The POL packaging structure of claim 17 wherein the first conducting shim comprises one of a metal and an alloy material. 